长江下游南京至贵池江段白鱀豚的观察

白鱀豚(Lipotes vexillifer)在长江下游自湖口至长江口都有分布。长江下游白鱀豚的生态观察始自1979年,但并未中断。其后南京至贵池间约250公里的长江段的观察,更有日本琉球大学名誉教授西胁昌治博士和鸟羽水族馆副馆长片罔照男于1981年3月15-21日参加了工作。现作简短报道。 1979年8月20日在太阳洲主航道中见到白鱀豚1头,次日该江段北岸群众两次发现白鱀豚在岸边游过。这一时期的白鱀豚不易跟踪观察,它们出水呼吸几次后,即消灭在远处。观察中也见到江豚(Neophocaena)10余头。1980年2月22日在太阳洲江段见到江豚两头,未发现白鱀豚。当天13:30在土桥附近见2头白鱀豚成体和1头幼体。它们在此活动了40分钟以上。2月24日返经太阳洲时见1头,白暨豚,另有4头江豚0 1981年春,联合考察船于3月15日自南京启航0 16日傍晚在芜湖附近的白茹沙江段见到江豚一群约10-12头,18日在接近土桥时又见到数头。19日上午在太阳洲见江豚一群约10余头。中午到达大通江面,先遇见数头江豚,接着见到一群带有幼体的白暨豚共约8-10头在近北岸处觅食。约40分钟后,此群离去,在附近又见到江豚6头左右。3月19日下午在梅龙和贵池及3月20日上午在梅龙也都见到江豚。据渔民报告,3月19日下午在白茹沙见到白暨豚在江中活动。1981年7月6日的观察中,在新港附近发现白暨豚2头,江豚3头。其中1头江豚背着幼豚。接着又在黑沙洲洲头附近遇见白暨豚3头。次日上午在近土桥外观察到白暨豚4头,江豚2头。     

让人欢喜让人忧——“水上熊猫”白鱀豚话题

1 白(既鱼)豚,庆祝香港回归的吉祥物白(既鱼)豚,在水深浪阔的长江中生活着的一种体态娇美、秉性独特的水兽,属鲸目、齿鲸亚目、喙豚科。据记载:其“大腹;喙小,锐而长;齿罗生,上下相衔;鼻在额上,能作声;少肉多膏;胎生;健啖细鱼。大者长丈余。”它是世界现有的五种豚之一,是中国的国宝,被称为“水中熊猫”;是真正的活化石。它在     

北京鸭视网膜节细胞的大小、密度和分布

采用Nissl染色法、视神经溃变法和神经元逆行追踪标记辣根过氧化物酶(HRP)法,研究了北京鸭视网膜节细胞(RGCs)的大小和密度及其分布的变化。北京鸭RGCs形态多样,有圆形、椭圆形和多角形等,RGCs总数为1.3×106个(P0),RGCs平均密度为5370个/mm2(P0),在视网膜中央有一个偏向鼻侧的高密度区即中央高密度区(8860个/mm2),由中央区至周边部,细胞密度逐渐降低,颞侧周边部最低(3440个/mm2)。不同区域RGCs大小差异显著,中央区以小细胞为主(62.2±23.3μm2,P0),而周边部RGCs逐渐增大,颞侧周边部最大(P0:133.7±75.7μm2;P8:152.9±55.9μm2)。由此可见,伴随RGCs大小由中央区至周边部的递增而细胞密度呈现递减的变化,这种变化趋势在颞侧周边部最明显。与此同时,随日龄增长,RGCs总数和密度均递减而细胞大小递增。dACs是位于视网膜节细胞层的小神经元,细胞大小为23.7±4.0μm2     

白(既鱼)豚MHC基因类DQB1座位第二外元的序列变异分析

测定了45个克隆的白(既鱼)豚(Lipotes vexillifer)MHC Ⅱ类基因DQB座位第二外元172 bp的核苷酸序列,共获得15种序列,发现了22个变异位点.核苷酸的非同义替换明显多于同义替换,并造成了15个氨基酸的改变.氨基酸的替换趋于集中在假定的与抗原的选择性识别相关的位点附近.白(既鱼)豚DQB基因的核苷酸和氨基酸序列与文献报道的白鲸(Delphinapterus leucas)和一角鲸(Monodon monoceros)DQB1序列具有较高的同源性.氨基酸序列不具备人及其它一些灵长类动物DQB2基因所共有的基序(Motif),而与牛DQB1基因的基序相近,说明本研究得到的白(既鱼)豚MHC序列应属于类DQB1基因.同一个体出现了多种序列的情况,提示白(既鱼)豚的DQB基因可能存在着座位重复.白(既鱼)豚的类DQB1座位的序列中存在多种基序的不同组合,推测是由于基因转换造成的[动物学报 49(4):501～507,2003].     

大白鼠视网膜中向同侧中枢投射的神经节细胞

在大白鼠视束和上丘注射HRP作逆行标记表明,向对侧中枢投射的神经节细胞遍布视网膜各处,而同侧投射的细胞大部分位于颞下侧边缘的新月形区域内,少数细胞分布在此区以外。与视束注射比较,上丘注射时同侧视网膜颞新月区内标记细胞数大为减少。统计测量表明,同侧投射细胞胞体直径平均比对侧投射细胞的略长。文中对上述结果的生理学意义进行了讨论。     

白暨豚保护研究的进展

白暨豚是一种仅存于中国的淡水豚,迄今已有约2500万年的历史。20年来,白暨豚的种群数量急剧减少。其数量从20世纪80年代初的约400头,锐减到90年代末不足100头。白暨豚的生存环境也急剧恶化,目前仅在长江中下游的干流中有分布。导致白暨豚濒危的主要原因源于日益增多的人类活动,包括水利工程、渔业活动、水体污染等。白暨豚的保护主要从3个方面进行：①建立白暨豚自然保护区,保护其自然种群和栖息地环境;②建立半自然保护区,实行迁地保护;③建立细胞库、基因库等,保护其种质资源。迁地保护为目前最为紧迫的保护措施。     

铜陵长江大桥对豚类栖息地的影响

根据1987-2001年在铜陵江段所进行的18次豚类生态考察,统计历年考察记录中,在成德洲-梅埂段（以下称大桥河段）工作的天数及观察到的白Ji豚和长江江豚数量,分别计算其SPUE值（Sightings per unit of effort,以头/d计）。并于1989,2001年,在长江水位8.5m左右（吴淞 高程）测定了大桥河段断面A,B,C,D的深度（m)及流速（m/s)。根据汉道最大河宽（B）,转折角（α）,曲折率（S/L）,以及汊道宽长比（B/S）的变化,分析河道与沙洲的变动对白Ji豚和长江江豚栖息地的影响。研究结果表明大桥建成后,河段平面变形小,汊道分流比稳定,滩槽很少变动,流态稳定,水势复杂多样,仍具备豚类栖息活动必要的水文条件,但铜陵大桥对其上下河道,沙洲也产生了一定的影响,主要表现为近期和悦洲与成德洲附近的滩槽冲淤明显,汇,分流区主流摆动不确定,不能形成稳定的水区,导致成德洲附近的白Ji豚和长江江豚活动次数明显减少,特别是白Ji豚的活动路线中（太阳洲→梅埂）的羊山矶,历次考察中未观察到白Ji豚,总而言之,白Ji豚在大桥河段的SPUE值降低与其种群急剧下降是一致的,但在梅埂活动的次数下降不明显;长江江豚在局部水域（梅埂,横港）的SPUE值有上升趋势,这些现象可能与近期的河床演变及桥墩挑流有关。     

崇安髭蟾视网膜的组织结构

在光镜和电镜下观察了崇安髭蟾视网膜的组织结构，着重探讨感光细胞和神经节细胞的形态，计数及分布。结果表明，其视网膜组织结构符合脊椎动物的基本模式。视我膜总厚度为１４３μｍ。感光细胞总数约２５０只，几乎全是视杆，似视锥的光感受器不超过３％。神经节细胞总数２１万，从节细胞等密度图上看出在视盘背侧沿鼻颞独有一个高密区，即视条。比较神经节细胞的密度分布及光 镜和 感光细胞形态结构及其分布，认为发髭蟾视网膜的     

半滑舌鳎仔、稚鱼视网膜结构与视觉特性

对1-50d半滑舌鳎仔、稚鱼视网膜和全长50mm的半滑舌鳎幼鱼视网膜结构和视觉特性进行了研究。结果表明:(1)3d仔鱼色素层形成,15d仔鱼没有显著的视网膜运动反应,25d时具有正常感受自然光的明视功能,43d半滑舌鳎稚鱼适应自然光的功能丧失;(2)半滑舌鳎仔鱼阶段感受细胞主要为高密度的单锥,视杆细胞和双锥细胞出现的较晚;单锥融合成双锥时,由于半滑舌鳎视锥细胞椭圆体细长,融合程度较差,尽管在视网膜横切面上能够看到双锥,但在切向切面上仍呈现单锥排列方式;随其生长发育,视锥和神经节细胞密度降低,视杆细胞密度增加,31d后视杆细胞数量显著增加;同时,外核层细胞核与神经节细胞的比值增大,网络会聚程度提高;相关数据表明,20-31d是视网膜结构和视觉特性发生明显变化的过渡时期,这是与半滑舌鳎从浮游生活到底栖生活生态环境的变化相适应的;(3)半滑舌鳎内核层结构特殊,50mm时只有1层水平细胞,属感光系统不发达类型,双极细胞和无长突细胞共4-5层,但不可分辨;内核层细胞层数的减少,基本上没有分化的水平细胞、双极细胞和无长突细胞,说明半滑舌鳎视网膜的光敏感性不高;(4)半滑舌鳎仔鱼浮游生活阶段视敏度较高,视觉在捕食行为中具有重要意义;底栖生活后,视敏度和光敏感性都较差,视觉在捕食行为中不可能具有重要作用     

根田鼠视网膜的胚后发育

视觉对动物的生活习性尤其是取食具有重要意义。本文对根田鼠视网膜的胚后发育进行了研究,结果表明:出生3d内根田鼠视网膜分化程度较低,神经节母细胞层尚未分化,占据了视网膜层的一半以上;5日龄时,外网层开始出现;6日龄时,外网层开始清晰,外核层与内核层更加清晰;18日龄时,视网膜结构与成年根田鼠结构相似,各层结构清晰可见。测量了神经节细胞层和外核层的细胞密度以及核层厚度,结果表明:随着个体发育,外核层细胞层厚度及细胞密度不断增加;而神经节细胞层厚度及细胞密度不断减少。与褐家鼠、黑线姬鼠、大仓鼠、棕色田鼠、甘肃鼢鼠、达乌尔黄鼠、岩松鼠视网膜相比,根田鼠视网膜结构介于夜行性与昼行性鼠类之间[动物学报52(2):376-382,2006]。     

Temporal and mosaic distribution of large ganglion cells in the retina of a daggertooth aulopiform deep-sea fish (Anotopterus pharao)

The daggertooth Anotopterus pharao (Aulopiformes: Anotopteridae) is a large, piscivorous predator that lives within the epipelagic zone at night. In this species, the distribution of retinal ganglion cells has been examined. An isodensity contour map of ganglion cells shows that the cells concentrate in a slightly ventral region of the temporal retina. The region of high ganglion cell density contains 4.07 x 10(3) cells mm(-2), and the resulting visual acuity is 3.5 cycles deg(-1). Outside the area centralis, conspicuously large ganglion cells (LGCs) are observed in the temporal margin of the retina. The LGCs are regularly arrayed, and displaced into the inner plexiform layer. Thick dendrites extend into the outer part (sublamina a) of the inner plexiform layer. In the retinal whole mount, the total number of LGCs is 1590 (90.7 cm specimen), and the mean size of the LGCs is about four times larger than that of the ordinary ganglion cells. The morphological appearance of the LGCs was similar to the off-type alpha cells of the cat retina. The function of these distinctive LGCs is discussed in relation to specific head-up feeding behaviour.     

Spatial Distribution of Excitatory Synapses on the Dendrites of Ganglion Cells in the Mouse Retina

Excitatory glutamatergic inputs from bipolar cells affect the physiological properties of ganglion cells in the mammalian retina. The spatial distribution of these excitatory synapses on the dendrites of retinal ganglion cells thus may shape their distinct functions. To visualize the spatial pattern of excitatory glutamatergic input into the ganglion cells in the mouse retina, particle-mediated gene transfer of plasmids expressing postsynaptic density 95-green fluorescent fusion protein (PSD95-GFP) was used to label the excitatory synapses. Despite wide variation in the size and morphology of the retinal ganglion cells, the expression of PSD95 puncta was found to follow two general rules. Firstly, the PSD95 puncta are regularly spaced, at 1–2 µm intervals, along the dendrites, whereby the presence of an excitatory synapse creates an exclusion zone that rules out the presence of other glutamatergic synaptic inputs. Secondly, the spatial distribution of PSD95 puncta on the dendrites of diverse retinal ganglion cells are similar in that the number of excitatory synapses appears to be less on primary dendrites and to increase to a plateau on higher branch order dendrites. These observations suggest that synaptogenesis is spatially regulated along the dendritic segments and that the number of synaptic contacts is relatively constant beyond the primary dendrites. Interestingly, we also found that the linear puncta density is slightly higher in large cells than in small cells. This may suggest that retinal ganglion cells with a large dendritic field tend to show an increased connectivity of excitatory synapses that makes up for their reduced dendrite density. Mapping the spatial distribution pattern of the excitatory synapses on retinal ganglion cells thus provides explicit structural information that is essential for our understanding of how excitatory glutamatergic inputs shape neuronal responses.     

Quantitative morphology of the primate peripheral retina (Macaca irus)

By using electron microscopy to study the quantitative morphology of the retina, it was possible to determine the spatial density of all principal retinal cells at a defined retinal location. In two retinas of cynomolgus monkeys at a position of 30 degrees nasal of the fovea centralis, the following cell densities were determined from composite electron micrographs: retinal pigment epithelium: 3,400 cell/mm2; rod cells: 115,000 and 168,000 cells/mm2; cone cells: 8,200/mm2; horizontal cells: 7,000/mm2; bipolar cells: 50,000/mm2; amacrine cells: 11,500/mm2; Müller cells: 16,000/mm2; and ganglion cells: 5,350 and 6,750/mm2.     

Retinal ganglion cell topography and spatial resolution in the smelt Hypomesus japonicus (Brevoort, 1856)

The present study deals with the topography of retinal ganglion cells (GCs) and spatial resolution in the smelt Hypomesus japonicus. The eyes and retinae were examined by light microscopy and computerized tomography. DAPI labelling was used to visualize cell nuclei in the ganglion cell and inner plexiform layers. Two zones of increased GC density in the nasal and temporal retina were bridged by a horizontal streak with the GC density ranging from 5600 to 8000 cells/mm². The maximum cell density (area retinae temporalis) ranged from 9492 to 14,112 cells/mm², and the total number of GCs varied from 286 x 10³ to 326 x 10³ cells in three individuals. The theoretical anatomical spatial resolution (the anatomical estimate of the upper limit of visual acuity) was minimum in the ventral periphery (smaller fish, 1.43 cpd; larger fish, 1.37 cpd) and maximum in area retinae temporalis (smaller fish, 2.83 cpd; larger fish, 2.41 cpd). The relatively high density of GCs and presence of the horizontal streak and area retinae temporalis in the H. japonicus are consistent with its highly visual behaviour. The present findings contribute to better understanding of the factors affecting the topography of retinal ganglion cells and mechanisms of visual adaptation in fish.     

Retinal ganglion cell topography and visual acuity of the sleepy lizard (<Emphasis Type="Italic">Tiliqua rugosa</Emphasis>)

The spatial distribution of retinal ganglion cells provides valuable insight into the importance species place on observing objects in specific regions of their visual field with higher spatial resolving power. We estimate the total number, distribution and peak density of ganglion cells in retinal wholemounts of the sleepy lizard, Tiliqua rugosa, a scincid lizard endemic to southern Australia. Ganglion cells were readily discernable from amacrine cells by their size and shape, prominent nuclei and the accumulation of Nissl-positive substances in their cytoplasm. A total of 1,654,200 (±59,400) presumed ganglion cells were estimated throughout the retina, distributed irregularly and forming a loose horizontal streak of high cell density peaking at 15,500 cells per mm². With a post nodal distance of 6.25 mm, we calculate an upper limit of visual acuity of 6.8 c/deg.     

Ganglion Cell and Displaced Amacrine Cell Density Distribution in the Retina of the Howler Monkey (Alouatta caraya)

Unlike all other New World (platyrrine) monkeys, both male and female howler monkeys (Alouatta sp.) are obligatory trichromats. In all other platyrrines, only females can be trichromats, while males are always dichromats, as determined by multiple behavioral, electrophysiological, and genetic studies. In addition to obligatory trichromacy, Alouatta has an unusual fovea, with substantially higher peak cone density in the foveal pit than every other diurnal anthropoid monkey (both platyrrhines and catarrhines) and great ape yet examined, including humans. In addition to documenting the general organization of the retinal ganglion cell layer in Alouatta, the distribution of cones is compared to retinal ganglion cells, to explore possible relationships between their atypical trichromacy and foveal specialization. The number and distribution of retinal ganglion cells and displaced amacrine cells were determined in six flat-mounted retinas from five Alouatta caraya. Ganglion cell density peaked at 0.5 mm between the fovea and optic nerve head, reaching 40,700–45,200 cells/mm². Displaced amacrine cell density distribution peaked between 0.5–1.75 mm from the fovea, reaching mean values between 2,050–3,100 cells/mm². The mean number of ganglion cells was 1,133,000±79,000 cells and the mean number of displaced amacrine cells was 537,000±61,800 cells, in retinas of mean area 641±62 mm². Ganglion cell and displaced amacrine cell density distribution in the Alouatta retina was consistent with that observed among several species of diurnal Anthropoidea, both platyrrhines and catarrhines. The principal alteration in the Alouatta retina appears not to be in the number of any retinal cell class, but rather a marked gradient in cone density within the fovea, which could potentially support high chromatic acuity in a restricted central region.     

Localization of the high-resolution area in the ganglion cell layer of the Baikal seal <Emphasis Type="Italic">Pusa sibirica</Emphasis> Gm.1788

The morphological and functional density of the retinal ganglion cells of the Baikal Lake endemic seal Pusa sibirica was studied using cresyl-violet-stained whole-mounts. An area of the highest concentration of ganglion cells has been identified by drawing up a density map. This was an ellipsoid spot in the upper temporal part of the retina 6–7 mm from the visual nerve output. The maximum cell density in this area was 3800 cells/mm². The retinal resolution estimated from the maximum density of ganglion cells and the posterior nodal distance (24 mm) was 2.4′ in the water and 3′ in the air, and this can be used as an estimation of the retina resolving power.     

Tracing retinal fiber trajectory with a method of transposon-mediated genomic integration in chick embryo

We report convenient retinal fiber tracing by transfecting the tracer cDNA by in ovo electroporation. Long-term and stable expression of tracer proteins such as green fluorescent protein is achieved by transposon-mediated genome integration of the tracer protein expression cassette. We carried out coelectroporation of a plasmid containing CAGGS-tracer cDNA flanked by the Tol2 transposable element along with a transposase expression vector to the optic vesicle of chick embryos at stage 11. By selecting electrodes, we can label a large group of retinal ganglion cells, or a small group of retinal ganglion cells; parallel electrodes assure transfection of large areas of the retina, and needle type electrodes label small areas of the retina. The retinal fiber trajectory and terminal zone (TZ) could be detected in the precise retinotopic manner on the contra-lateral side of the optic tectum. The method has advantage in that we can show the retinal fiber trajectory in relation to the molecules that are responsible for pathfinding for the retinal fibers in the same specimen.     

Axonal pathfinding in organ-cultured embryonic avian retinae

Eye cups from stage 14-28 (E2 to E5) chick and quail embryos consisting of neural retina, lens, and vitreous body were cultured for 1 or 2 days. These eyes expanded by proliferation of the retinal cells and the surface areas of the retinae increased several-fold. The area covered by ganglion cells and axons also expanded in vitro. [3H]Thymidine labeling showed extensive proliferation of the neuroepithelial cells including the formation of new ganglion cells. Culturing eyes from embryos before stage 17 results, as in vivo, in the generation of the first ganglion cells of the retina, but unlike in the in vivo situation, the outgrowing axons always formed a random fiber net in the central portion of the retina. A defined axonal pattern identical to the in vivo developed only in specimens from embryos of stage 17 and older. Some aberrant axons, however, were also observed at the retinal periphery in specimens from embryos of more advanced stages (20-24), but only during the second day of culturing. Axons in retinae from embryos of stages 23 to 26 heading toward the optic fissure often crossed the fissure and, in contrast to the situation in vivo, invaded the opposite retinal side. These axons of wrong polarity followed the pathways of axons growing centripetally but in reverse direction. This suggests that the polarity of growing nerve fibers and their course are determined by different factors. Culturing the eyes of embryos from stages 20 to 25 in the presence of antibodies showed that the antibodies penetrated the entire retina with 6 hr. Neither anti-N-CAM nor the T-61 antibody--both recognizing membrane proteins of retinal cells--affected the growth of the eyes in vitro. The development of the axonal pattern in vitro was not affected by incubation with N-CAM-antibodies at concentrations up to 500 micron/ml, whereas the T-61 antibody which is known to block neurite extention in vitro (S. Henke-Fahle, W. Reckhaus, and R. Babiel (l984). "Developmental Neuroscience: Physiological, Pharmacological, and Clinical Aspects," pp. 393-398. Elsevier, Amsterdam/New York) showed inhibition of axonal growth in retina cultures at 50 micron/ml. These results indicate that the eye cultures can be used as a test system for antibodies against antigens which could be involved in axon extension and neurite pathfinding in situ.     

Functional anatomy of the photoreceptor and second-order cell mosaics in the retina of Xenopus laevis

Mosaics of photoreceptors, and horizontal and bipolar cells of the Xenopus laevis retina were studied in whole-mount preparations applying lectin-cytochemical, immunocytochemical and intracellular labeling techniques. The combined density of all photoreceptor types was about 13700/mm2, of which rods represented 53%. Of the cones, the large long-wavelength-sensitive (86% of all cones) and the miniature ultraviolet-wavelength-sensitive (4%) ones could be labeled with peanut agglutinin, whereas the large short-wavelength-sensitive (10%) cones remained unlabeled. There were no significant regional differences in photoreceptor distribution. Bipolar cells were selectively labeled with antibodies against calretinin. Their density was between 4000 and 6000 cells/cm2, with slightly elevated numbers in the superior nasal quadrant. Two types of horizontal cell were injected intracellularly. The luminosity-type cells were more frequent (approximately 1000 cells/mm2) than the chromaticity cells (approximately 450 cells/mm2). The dendritic field size of the latter cell type was threefold bigger than that of the luminosity cells. The coverage factors were estimated to be 3.3 for the luminosity cells and 5.2 for the chromaticity cells. The luminosity cells contacted all photoreceptor types, whereas chromatic horizontal cells received their inputs from the short-wavelength-sensitive cones and from some, but not all, rods. Luminosity cells encounter about 50-60 potential synaptic partners within their dendritic fields, whereas chromatic horizontal cells only about 20. Chromatic horizontal cells form multiple synaptic contacts with the short-wavelength-sensitive cones. The results indicate that the overall photoreceptor to bipolar and bipolar to ganglion cell convergence in Xenopus retina is similar to that in the central retinal specialized regions of mammals, predicting comparable spatial resolutions.